text:
Should helicopters fly when they the lack power for vertical climb out of ground effect?
Following up on this question: If a helicopter lacks power to climb vertically (i.e., with no translational movement) out of ground effect, is it ever considered safe to fly?  If so, under what conditions?
Or is the hover capability of a helicopter generally considered to be independent of its safe flight envelope?

What is missing from my answer to the question you linked?  If you don't have enough power for an OGE hover, then you can use translational lift out of an IGE hover.  It's perfectly safe.  See this, especially the power required curve.

@Simon - Your other answer doesn't address whether there is a relationship between hover capability and safe flight.  Also, you said it's possible to do a running take-off in conditions where HOGE is not possible, but not whether it's always OK.  Based on your comment it sounds like it is always OK, and the one has nothing to do with the other from a safety or operating perspective.

Up to a certain speed, which will be in the POH, the greatest power requirement is when hovering out of ground effect.  Next is hovering in ground effect and power required in forward flight is the lowest, and decreases up until a point where the increase in parasitic drag starts to increase the power required.
See a typical power required curve.

From the AOPA blog
So it is possible to not have enough power margin to be able to hover OGE but enough to hover IGE.
To perform a normal take-off (ignoring a lot of side effects such as need for pedal), come to a normal hover height, about 2-3 feet, then push the cyclic forward.  Increase collective smoothly to maintain altitude and allow the aicraft to accelerate which it will, since increasing collective increases power and the rotor thrust now has a forward horizontal component. As significant translational lift kicks in at about 10 kts, a reduction in collective is required to avoid climbing early.  You don't want to be climbing with high pitch, and therefore high drag, if the engine quits.  When reaching about 45 kts or so, pull back on the cyclic to adopt a climbing attitude.  The aircraft will settle at about 65 kts.
To perform a "creeping" take-off, increase collective to become light on the skids.  Gentle forward pressure on the cyclic will start a slide on the ground. As translational lift kicks in, apply a little back pressure to lift gently to climb to about 1-2 feet to remain in maximum ground effect and continue to accelerate.  Wait until 45 kts is reached, and off you go.  During this manouver, the collective is left where it is until established in the climb, aside from small adjustments needed to keep the altitude constant during the creep.
I am not sure if it is a certification requirement, but every helicopter I've flown is capable of safely flying when there is not enough power margin to hover OGE, and most helicopters I have flown are on the weak side (R22, B206, B206L, S300, Enstrom 280) so I guess all helicopters can do so.
I checked a few types certs and I can see nothing about creeping take-offs. I am reasonably sure that the only limits that apply are for RPM, MAP, torque, N1, N2, temperatures etc. As long as you don't exceed those and are in accordance with the POH, then it doesn't matter how you get airborne. As you can see from the power required curve, the power required for forward flight is a great deal lower than for hover.
I've copied in your comment:

I understand that vertical climbing is not hovering, but neither is it
  "flying" in the same sense that translational flight adds lift.
  Positive vertical climb out of ground effect with no translation is, I
  deduce, the hardest thing a helicopter can do. The maximum rate of
  climb in that attitude seems like something you'd have charts for, but
  I don't even know a term or acronym for it.

Because of translational lift, a helicopter requires less power to climb when flying forward than it does to hover, in or out of ground effect.  The greatest power requirement is when hovering OGE and increasing the hover height requires more power still so yes, climbing vertically OGE requires more power than any other regime.  There is no chart, or term for this that I am aware of simply because you should not do it and the POH will detail restrictions, not least, the "dead mans" or avoid curve.

http://flyinghelicoptersinalaska.blogspot.co.uk/2010/04/why-dont-helicopters-go-straight-up-and.html
The only time you should ever climb vertically (a "towering" take-off) is when operating out of a confined area when it would not be possible to get out without clearing the trees, walls or whatever.  Some pros do it all the time, e.g. power line inspection/repairs, logging and so on but they accept a risk of operating outside of the limits and are certified and insured appropriately.
The avoid curve shows the combinations of height and speed in which test pilots (i.e. the best) have demonstrated that a safe landing is possible if the engine quits.  You should not fly in the shaded area so you can see (and that chart is similar for all helicopters) that a towering take-off should never be used unless there is no alternative, and only then, for the shortest possible time.  Coming into a high hover, say 50 feet, or continuing a vertical climb OGE is prohibited by virtue of it being in the shaded area(s) of the chart.
Helicopters are not always intuitive.  Many people are surprised by the fact that climbing needs less power than hovering, and the faster you go (up until that point where the parasitic power increases dramatically), the less power is required.  Imagine a car where less power was required to accelerate and go faster!

Can you briefly explain the reason for the small shaded area < 20' and > 50 kts? Thanks!

@RalphJ Do you mean the bit in the lower right, from 45 kts and faster up to about 18 feet?

@Simon: I'd guess that's the region where an engine failure in still air might cause you to contact terrain excessively fast?  If you're below 45kts you're not excessively fast, and if your above 20 feet you'll have time to pitch the helicopter to trade speed for elevation until your speed is below 45kts?  How would wind speed affect that?

@Simon Yes, that region. Is the concern pitch sensitivity? Engine failure? Something else? Thanks!

@RalphJ Engine failure.  At that speed, if the engine quits, the nose will pitch down and you will be on the ground, with no control and high speed, before you know what's happened.

@supercat You don't trade speed for evelation, you trade speed for rotor RPM.  Rotor RPM is life.  You simply can't climb since the only thing that can keep the rotor spinning is airflow coming up through the disc as you descend or, flaring to convert speed to RPM.  The speeds on the chart are airspeeds so wind speed doesn't matter until you need to land when the stronger the wind, the easier the landing as you will have lower groundspeed for any given amount of lift.

@Simon: You're right; my point about the trade-off, though, was mainly that the goal is largely to get rid of the kinetic energy--not necessarily get anything in return.  If you're 20 feet off the ground and you suddenly lose all kinetic energy and engine power, you'll simply hit the ground after a 20 foot drop--not good for the craft, but should be survivable for the occupants.  If you were  traveling at 80mph horizontally and hit the ground still traveling at 80mph I would think that would be much worse.  With regard to wind...

...I would think that being 5 feet above the ground with a 50kt airspeed flying into a 25kt wind would be better than being 18 feet above the ground with a 45kt airspeed flying with a 25kt wind since in the former case you don't need to do anything to get your ground speed below 45kts, while in the latter case reducing ground speed to 45kts would require reducing air speed to 20kts and even there I would think a 45kt landing with a 25kt tailwind would be harder than a 45kt landing in still air.

@supercat If you try to land from an autorotation downwind, then a Darwin award awaits you.  Please read a few articles about the mechanics of autorotations.  Your assumptions are wrong.  A landing from an autorotation should be 15 kts or loss.  Anything more and you'll lose control.  The only thing that matters is RPM and energy management.  Groundspeed only matters in the last 30 feet or so.  You lose speed by flaring, not by "trading speed for elevation" which in any case, is impossible.

@Simon: Ralph had asked about the shaded region to the lower-right corner of the picture, and I was curious about it too and wanted to test my intuition.  My interpretation is that in still air, if you're traveling below 45kts and lose power you'll survive even if you contact terrain and if you have 18 feet of elevation to play with you'll be able to--via whatever means--avoid contacting terrain until your airspeed is below 45kts.  My intended question was whether one would need additional altitude for safety while traveling downwind.

@supercat My last response, since you don't appear to be understanding what I'm saying.  18 feet, you have nothing to play with.  Either you have flared, checked and arrested the descent, or you will crash.  There are no "whatever means". A 45 kt autorotation landing is at best, a bad crash, most likely fatal and you do not land downwind from an auto, ever. I've explained what the shaded areas are.  They are the areas from which it is not possible to land safely following an engine failure.  Please do read about autorotations since your understanding, and your "intuition" are wrong.

@Simon: The chart seems to suggest that it's safe to be 19 feet from the ground while traveling at 140kts (presumably over an unpopulated area).  Am I misreading it?  Should the gray area extend upward at higher speeds?

@RalphJ - Sounds like a good question that deserves an elaborate answer.  I posted the question here.


text:
Why is there a plateau in helicopter H/V diagrams?
The "dead-man's curve" in a typical helicopter height/velocity (H/V) diagram is commonly referenced to indicate that "towering flight" is dangerous and avoided in general practice.  (Simon explained, "The Avoid curve [outlines] the combinations of height and speed in which test pilots (i.e., the best) have demonstrated that a safe landing is possible if the engine quits.")
But H/V diagrams also have second envelope that is marked for avoidance.

I don't know if this area in the lower right has an ominous name: If not perhaps we should call it the "dead-man's plateau?"
But why is it considered unsafe to fly at extremely low altitudes at indicated airpseeds above about 50 knots?
In a comment on this in the answer above Simon says, "At that speed, if the engine quits, the nose will pitch down and you will be on the ground, with no control and high speed, before you know what's happened."
Can someone elaborate on the dynamics of this?  Why would the nose pitch down abruptly if the engine quits?  If that's such a reliable effect would it not be trivial and worthwhile to have a torque-driven spring that bears on the cyclic, so if torque suddenly changes then the cyclic is just as suddenly nudged backwards?
In any case, one is left wondering if the full answer isn't more nuanced: The most striking characteristic of the dead-man's plateau is that it appears to be the height at which one enters ground effect.  Is there some other aerodynamic phenomenon at play in high-speed ground effect flight?

You might edit into your question that, according to Simon on the other question, that chart is specific for engine failure.

@TomMcW No.  The curve shows the areas where you should not fly when the engine is running because you cannot land safely from there if the engine fails.  It is not "specific to engine failure".

@Simon I guess I worded my comment wrong because that's what I was trying to say. The shaded areas would be a problem specifically IF the engine fails. You had another chart on the other question that showed (I believe) where you will not have enough power even with the engine running. I was just suggesting it would be good to include that info with the chart in the question. It's ok the way it is though, still pretty clear what he's asking.

As speed increases, most helicopters pitch up.  This is because the lift generated on the side of the retreating blade gets progressively less than the lift generated on the advancing blade side.
Due to precession, the effect of this is felt 90 degrees later so instead of rolling to the left (or right, depending on which way the blades rotate) because of the dissymmetry of lift, the tail drops, therefore pitching the nose up.  Whether this happens on a particular helicopter, and by how much, depends largely on the pitch stabilisers.  However, helicopters are naturally unstable in pitch.  You cannot take your hand of the  cyclic and maintain a constant attitude, absent any autopilot or other automatic assistance.
As the helicopter accelerates, the pilot subconciously counteracts this by applying foward cyclic pressure.  The higher the speed, the more forward pressure is needed to maintain altitude and the helicopter flies nose down.  You fly a helicopter by "sight picture" to such an extent, that to accelerate, you pitch the nose down to give you the "65 kt picture", or the "100 kt picture", allow the aircraft to accelerate to the desired speed, then trim.  The nose is pitched down a lot at 100 kts compared to say 50.
When the engine quits, assuming it's an instantaneous failure, there is nothing to stop that forward pressure forcing the nose down and at such low heights and high speed, losing 18 feet of height before the pilot reacts and pulls back to flare would be easy.  Even if they react really quickly and flare without losing much more than 5 or 10 feet, there is a very real risk that the tail will strike the ground and at those high speeds, that will result in a really bad crash.
Let's assume that everything goes right. There is no time at that height to lower the collective and raise it again.  You will also have a lot less than a second to flare so will lose very little forward speed.  In the best case, you are going to land at 50 kts or higher with the collective in your armpit and the rotors already stalled, if not stopped altogether, and this is at best a bad crash, quite possibly fatal.
The most important thing to remember is that the shaded areas represent the flight regimes where test pilots, with instant reactions since they initiate the manoeuvre, cannot demonstrate a safe landing with no damage.  This is at the edges of the shaded areas and once they get to the point of saying "one more foot, and we would not have had a successful landing", they stop exploring the envelope and draw the curve in the POH.  To add a safety margin, the tests are done at max weight.  Even so, the wise pilot will give those areas a wide berth whenever possible.
Why isn't there some automatic device to pull the cyclic back?  Because you do not do this if the engine quits when in a hover or up to about 10 kts at low height.  In the avoid area you ask about, it would need to pull, then push to level the skids again in the blink of an eye.  It's different when hovering at 1,000 ft and different again if doing 90 kts at 1,000 ft. And that's before we add all the variables - pressure altitude, temperature, wind strength and direction.
To deal with all of this, you would need a very clever system loaded with sensors.  Most people call such systems "pilots".
I would rather just avoid the shaded areas.  It's no big deal.

Does the pitch down moment happen at the same rate regardless of speed? It just seems odd that the height requirement is the same at 55kt as it is at 150kt.

I don't really know.  My guess is that they stopped exploring the envelope.  No-one in their right mind (except perhaps the military) is going to fly at 18 feet and 150 kts.

i call BS on the pitch-down moment part of this answer. The bottom right part of the H-V diagram is there because  below a certain altitude, the pilot simply can't do a quickstop without striking the tail because the nose is so low.

@rbp  Indeed that's why the bottom right part is there, but the nose will pitch down as the induced flow is lost and the relative airflow changes to come up from beneath which strikes the stabilser and causes a pitch down moment. Wagtendonk and Bailey both have details on this.

"You should avoid the low altitude, high airspeed portion
of the diagram (section B), because your recognition of an
engine failure will most likely coincide with, or shortly
occur after, ground contact. Even if you detect an engine
failure, there may not be sufficient time to rotate the
helicopter from a nose low, high airspeed attitude to one
suitable for slowing, then landing. Additionally, the
altitude loss that occurs during recognition of engine failure
and rotation to a landing attitude, may not leave
enough altitude to prevent the tail skid from hitting the
ground"

nothing about the nose tucking because of loss of induced flow. please provide an on-line reference

@rbp I tried to find online references which you would accept, which I take to mean printed excerpts of Wagtendonk, Bailey, Prouty etc but couldn't find anything quickly and don't feel compelled to do so to support someone questioning a fact.  Lever down,pitch down, simple.  Googling for primary and secondary effects will give you multiple references and this discussion on PPRuNe also provides jumping off points.

The point about removal of the induced flow is that the rotor flaps forward (since you are holding forward cyclic pressure to counter blow back) and without the induced flow, or at least, less of it, the rotor will also tilt forward since the angle of attack of the advancing blade, especially in the 4th quadrant, is rapidly reduced.

That could all be true. None of the on-line sources I looked at it mentioned loss of induced flow, and I guess you couldn't find it either.

The prune article is very good, and highlights our agreement to pull back on the stick (for whatever reason).

@rbp  Ok, so the cause might be debatable, and next time I am in my store room, I will dig out my dusty copy of Wagtendonk because he does talk about the effect of a sudden removal of flapback, but the fact remains that the nose tucks in on collective drop.  Just try it!  Next time you're cruising, drop the collective assertively but not enough to split the needles and see what happens.  You will adopt significant nose down instantly.  And yes, we agree on the need to pull the stick back.

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text:
Why don't helicopters prefer shorter rotors with more blades?
My understanding of helicopters is that, despite theoretically increasing efficiency, longer blades are worse in practice than short ones in every respect (except, perhaps, cost):

Longer blades are more prone to vibration and resonance dynamics, if for no reason other than that their rigidity is reduced by length, holding all else constant.
Longer blades provide less operating clearance.
Longer blades not only stall before shorter blades (retreating), but also hit the Critical Mach number at lower air speeds (advancing).
Fewer blades require higher rotational speeds for a given "rotor disk" area, which is inefficient from not only an aerodynamics perspective but also, presumably, a transmission-and-control perspective.

But all helicopters have few blades of significant length.  So: What are the advantages of longer blades, or disadvantages of shorter blades, that lead to the rotor designs in common use?
I would imagine that in the limit it would be optimal to run something more like a ducted turbine segment, where the swept area is virtually covered in blade surface (i.e., maximizing the number of blades over the swept disc).
Noting that in practice blade size seems somewhat proportional to the body size of the aircraft, I'll deduce that in practice the bulk of the downforce needs to be generated some minimal distance away from the aircraft's body, though with some attention to the body's vertical aerodynamic aspect it seems like that could be reduced.  I guess tilt-rotors could support this hypothesis since their rotors are positioned at a distance from the body and they use smaller rotors, although it seems like they still use blades as large as possible given the wing size and body configuration.

@fooot - The best answer to that question is inspiration for this question; it does not answer it (as far as I can tell).

@feetwet, that answer, among other things, states that “…improve efficiency, which you could do by making the blades longer”.

voting to leave this question open. The question is more precise, and it attracted better answers that the other inspirational question

@JanHudec - Just edited to clarify that I'm asking about everything except that one point in favor of long blades.

Also related: What is the relation between a helicopter's length and rotor diameter?

To an engineer "better in every way except efficiency" roughly translates to 'worse.' Operators tend to translate it that way, too.

@reirab - I'll emphasize the theoretical efficiency: If you don't get theoretical benefits in practice they aren't worth anything!

@feetwet Who said we don't see the benefits in practice? The whole point of having theory is to describe what we would expect to see in practice.

@feetwet, A smaller diameter rotor with a lot of blades rotating slowly can stall like the wings of a plane. So you can not increase the number of blades reducing the RPM and the propeller diameter (to keep the power and thrust constant) because you propeller will reach the stall point.

@Energizer777 - Thanks, I didn't know that was a factor -- or at least one that couldn't just be designed away with more aggressive blades.  Might be worthy of an answer in itself if you can explain when/why design limits can't cope with lower RPM.

The rotor works by accelerating air downwards, therefore creating an upward reaction force on the blades that lifts the craft.
The lift force is equal to
$$L = \dot{m}\Delta v$$
where $\dot{m}$ is mass flow rate through the rotor and $\Delta v$ is the change of speed of the air. To accelerate the air to that speed, it has to give it kinetic energy. This requires power
$$D = \frac12\dot{m}\Delta v^2$$
(the induced drag).
Now a rotor with smaller diameter will be able to affect less air, so the $\dot{m}$ will be lower. To produce the same lift, it will need larger $\Delta v$ and therefore it will need more powerful engine (up to a point, because longer blades will have higher form drag that will eventually outweigh the reduction in induced drag) and, more importantly, burn more fuel.
The blades, like wings, affect air to a significant distance above and below them, so you don't need many blades to use all air within the rotor area. But no matter how many blades you add, they will still only affect the air within the rotor area, so the efficiency won't change much.
As far as tiltrotors go, they have relatively small rotors and that makes them awfully inefficient in hover. But they don't spend most of their time hovering, they spend most time flying somewhere and in the fixed-wing mode they are faster and more efficient, which outweighs the worse efficiency during take-off and landing.
See also: Is there any equation to bind velocity, thrust and power? (via Energizer777's deleted answer).

So the efficiency of a rotor blade is proportional to its length?  Meaning the only reason powered rotary wing aircraft ever use more than two main blades is because they have reached some structural limit on their blade length?

@feetwet, the blade length is (in addition to structural strength) limited by tip speed and then only so much lift can be generated by single blade, so more blades are needed for higher lift (and thus capacity). But efficiency is proportional to the rotor diameter, so larger rotor is preferred, because it provides lower fuel consumption and thus longer range and lower operating cost.

The number of (main rotor) blades in a helicopter are dependent on a number of parameters; Usually there are some major issues with having a large number of blades in a helicopter though:

One main reason is efficiency- In general, lesser the blades, more efficient the system- as it changes the momentum of more air mass i.e. accelerates more air by a lesser amount (akin to the bypass of turbofan engines).
In general, the performance of the helicopter rotor system is affected by solidity (i.e the ratio of blade area to total disc area) rather than the number of blades.
As the number of blades increase, the interaction of subsequent blade with the advancing blade's vortex increase (i.e the blade flies into the preceding blade's wake), which affects the lift produced.
More blades means more complex rotor hub (more parts usually translate into more problems- maintenance and otherwise) and more interference in the inboard region of the blades. Also, the rotor hub drag is increased.
One thing you're missing is that the blade velocity $V$ (in $L \ = \ \frac{1}{2} \ \rho \ V^{2} \ S$ ) is in itself dependent on the blade length (and rotational speed, through $V \ = \ R\omega$). This means that as the blade length reduces, they have to rotate proportionally faster to produce the same lift- thus in reality, the tip speeds of smaller blades will be more. Usually, the inner third length of a rotor blade contributes very little to lift.
As far as vibration is concerned, (though it is better to have more blades) the whole rotor system has to be taken as a unit rather than as individual blades and the most important consideration is the rotor speed and its harmonics rather than the blade length.

Holding all else constant, my assumption is that a reduction in disc area (due to shortening blades) can be compensated by the addition of blades instead of by an increase in rotational speed.  I assume, based on the density of blades in efficient turbine fans, that wake interference is a solvable problem, even if it requires a stator or something like that?

Regarding the rotor hub drag and complexity: Is this entirely an artifact of aircraft motion translational to the rotor plane, and the need to change each blade's angle of attack throughout a single rotation during translational flight?  If not, then what?  Because even variable-pitch propellers don't require extraordinarily complicated or large hubs.

@feetwet - The fifth point above explains why that assumption won't hold.  The tips of the blades travel faster than the portion closer to the hub.  The difference in velocity is linear based upon rotor diameter, however the amount of energy (and hence, the amount of lift/thrust) grows with the square of velocity.  So to cut your rotor diameter in half without adding rotational speed, you need 4x the number of blades.  That's if you can keep the mass of your craft exactly the same.  Realistically your mass would increase, meaning either even more blades, or more rotational speed.

The blades of a helicopter are long, narrow airfoils with a high
  aspect ratio, a shape that minimizes drag from tip vortices (see the
  wings of a glider for comparison). They generally contain a degree of
  washout that reduces the lift generated at the tips, where the airflow
  is fastest and vortex generation would be a significant problem.

source: Wikipedia.

Hence a larger number of blades moving more slowly would be attractive, right?  This seems like an elaboration of point #4 in the original question.

@feetwet, no, they wouldn't, because the thing that minimizes the “drag from tip vortices” (the vortices are effect, not cause of the drag) is the span.

@JanHudec - maybe this warrants a separate question, but isn't unmitigated tip vortex an artifact of long blades?  With sufficiently short, rigid blades presumably one could add wingtip devices to counteract tip vortex?  Or, in the limit, use a ducted rotor (as suggested in the original question)?

@feetwet, no, the vortex is simply result of the fact that the air within the rotor diameter is accelerated downwards and the air outside of it is not. And, as I explained in the other answer, smaller rotor needs to accelerate the air to higher speed, causing stronger vortices (Site note: ducting does not change the picture much; there are still two air masses of different velocity).

@JanHudec - Are you sure?  My understanding is that wingtip vortices which reduce wingtip lift and waste power creating "washout vortices" are a function of air being allowed to slide centripetally over the end of the airfoil, and that those losses can be significantly mitigated using wingtip barriers.  Of course downwash vortices are a separate phenomenon that are primarily a function of the rotor speed.  But as suggested elsewhere here: to first order, for a given rotor disc area and blade speed one can increase downforce without increasing rotor speed by adding blades, right?

@feetwet, I have never ever read or heard separating “wingtip” and “downwash” vertices. It is really a single vortex, which is caused mainly by the downwash and in a little part by the transverse flow. The contribution of the transverse flow is at most a few percent.

@JanHudec - Again, consider the extreme case of propellers: Once they reach a certain speed they need a duct ring, which is really just a closed wingtip, and at that point there is no tip vortex.

@feetwet, Yes, there is still a vortex. It is not a wingtip/proptip vortex any more, because it is around the duct rather than around the tips, but it is still a vortex and its total energy is basically the same, only little bit smaller because the duct displaces the high-speed core.

@feetwet, besides, if you mean the fan of a turbofan, the purpose of the duct is not to eliminate any vortex. The purpose is to slow the oncoming air (converting its kinetic energy to pressure (=potential energy)) so the fan can work at flow speed it can manage (~M0.5) and then convert the pressure back to kinetic energy in the nozzle.

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text:
What is the ASTERIX terminology for an atomic piece of information?
The ASTERIX standard defines the smallest piece of metadata information:

Data Item: The smallest unit of information in each Data Category.

And the implementation equivalent:

Data Field: Physical implementation for the purpose of communication
  of a Data Item, it is associated with a unique Field Reference Number
  and is the smallest unit of transmitted information.

But, neither of them are atomic. The most common example is Data Source Identifier (SIC/SAC) which contains two pieces of information: SIC and SAC. For instance, such a Data Item is defined in the 048 Category:

Data Item I048/010, Data Source Identifier Identification of the radar
  station from which the data are received. Two-octet fixed length Data
  Item.
  bits-16/9 (SAC) System Area Code
  bits-8/1 (SIC) System Identification Code

So my question is: what is an atomic (minimal) piece of information called in the ASTERIX standard?

There is no official name for that unfortunately. I call it element.

The spec does not appear to define what is an atomic piece of information, likely because it assumes the implementer already knows the answer. From what I see, the equivalent of what you seek from the point of view of the spec is the data item.

Can someone please edit this to make the relationship to aviation apparent?

@MichaelHall I added usage guidance and wiki entry to the [asterix] tag. That should make the relationship to aviation clear. Note that our on-topic help center page includes air traffic control.

@Bianfable, I don’t see “air traffic control” anywhere in the question.  If that is the connection, a simple one line sentence in plain language would be nice.  Otherwise this seems as relevant as asking a question about aluminum atoms.  (Airplanes are made of aluminum, so…). This ties in with our other commentary about the relevance of atmospheric questions.  I realize we all come to this site with different aviation experience and interest, but I should have to perform research just to get a high level grasp of of the what the question is about.

There are many questions here that go way over my head, but I can at least recognize the relationship to aviation and know when to pass, or when I might offer some good insight.  I’m not asking for much here, something as simple as “the ASTERIX standard for developing air traffic control software code…” would establish the connection.

Hello @MichaelHall, There are no objections from my side to modifying the question or removing it at all. But first I think we need to clarify if surveillance radars and their communication protocol can be considered as part of the "Air Traffic Control" topic?

Is this question about surveillance radars and their communication protocol?  Because if it is, then simply state that and I will just shut up and sit down.  But “atomic piece of information”?!

@Gluttton please edit your question as requested, so that it is more accessible for readers without prior knowledge of the subject.

Although this term is not used, you can call each piece under data item is a data field.

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text:
Are any flight schools or clubs in Canada using Pipistrel's Alpha Electro or Velis Electro?
I'm interested in the business and environmental possibilities of using electric trainers for training.
Are there flight clubs or flight schools training with electric aircraft?
I thought I'd read that Canada provided some kind of type rating for the Alpha Electro, and I'm hearing that Pipistrel's newer Velis electro is certified (at least in Switzerland).
Is anyone doing this now in Canada? If not, why not? Are there regulatory obstacles?

Welcome to AviationStackExchange. One drawback to using an electric aircraft in training is the issue of critical mass. There are not enough electric aircraft in the rental and General Aviation inventory to make training in one attractive. I for one would not find it attractive as a student to train in a type of aircraft that I have very little likelihood of flying outside of training.

Thanks Dean! Appreciate the thoughtful answer.

I really hope we start seeing more electric aircraft. It would be so much more efficient.

The only Pipistrel Electro registered in Canada is an Alpha, C-IZAP, registered to a private owner in British Columbia.  So the answer is for now, no.
Pipistrels, including the Electros, are licenced in Canada as Advanced Ultralights.  I don't see any reason an Electro couldn't be used for training under the Advanced Ultralight regulations (not for Private Pilot however).  Probably cost is an obstacle.

The University of Waterloo has imported Canada's first Pipistrel Velis Electro. This one is for testing, but hopefully it leads to certification and flight schools like our partner Waterloo Wellington Flight Centre will introduce them more widely.
Paul

OOOOOhhhh cool... thanks Paul! Any clues as to where I might look to spot such an unusual creature?

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text:
During spin recovery, can you just release the yoke/stick to neutralize the ailerons?
I have been watching spin recovery videos on YouTube for the last few days. Scary stuff and I haven't even started flying yet :o haha
Anyway, the recovery seems to be commonly described as PARE:

Power idle
Ailerons neutral
Rudder opposite of spin
Elevator forward

Do you physically neutralize the ailerons or does releasing the yoke/stick do that? Is that specific to certain airplanes?

Throttle to idle, then do nothing!  In the US, the FAA requires all certified aircraft to come out of a spin within 1-1/2 turns. It is recommended the throttle be placed in idle and all that is necessary is for you to take your hands off the controls. So, throttle to idle - and do nothing. The aircraft will recover in a nose dive, and you will then be required to pull out of the dive.

@jwzumwalt - I agree with you, if you have enough altitude to recover, if your CG is not full aft, and if you can pry your hands and feet from the controls while the aircraft is doing something unexpected.  A hands off recovery will consume a lot of altitude.

Typical altitude loss is 500ft per turn. Typical manual recovery is 1/2 to 1 turn - if you do it right, otherwise wrong inputs aggravate the spin. So, yes you can save at most 200-500ft altitude with proper execution. However, to say, "if your CG is not full aft" is not correct - FAA requires the maximum 1-1/2 turns for the entire legal CG range. If a person flies illegal, they are playing Mr. Test Pilot and all bets are off anyway.

You're combining two different techniques.
Using PARE, you physically neutralize the ailerons. Look down if necessary to ensure the yoke is level with the dashboard or the stick is centered left/right.
Once the ailerons are neutral, you continue on with rudder opposite the spin (look straight forward, not out to the side!) and elevators.
In some aircraft, it's possible to recover the plane simply by pulling power to idle and removing your hands and feet from the controls.
As always, get competent instruction from someone with experience in your spin-rated aircraft before trying this on your own.

Hmm why do these answers differ from the comment of "jwzumwalt" above?

@Fattie - OP didn't restrict his question to certified aircraft only and asked about how to neutralize the ailerons while using PARE.  The PARE technique does not include letting go of the controls.

@Dan Pichelman I had thought of a -1 but held back because rightfully this list is international and as you point out was not specific to certified aircraft. I believe this list regularly splits hairs and minces words far to often. But, after consideration of your comment, it has merit. This is a gentle reminder from my own painful experience on this list that it is a good idea to carefully (narrowly) qualify answers with exactly what aircraft or country you use as a base of reference. Note that I used FAA, certified, and US...

You do not want to put aileron inputs during a stalled condition, as this can induce and/or further aggravate a spin.  So a neutral control position should be assumed with the stick prior neutralizing the spin with opposite rudder input.
Spin recovery techniques vary a little between manufacturers and specific aircraft but the PARE method (Beggs/Muller technique) is one of the most common recovery methods out there.  Alsways use the approved spin recovery technique listed in your airplane’s AFM.

The Beggs-Muller ‘Emergency Spin Recovery’ method which Gene Beggs wrote specifically for the Pitts Specials is…
Throttle to Idle, Let Go of the Stick, Apply Full Opposite Rudder to the direction of yaw - as determined by sighting down the top of the engine cowling at the ground.
Gene says that after thousands of spins that this method will stop any spin in the Pitts whether upright or inverted, flat or accelerated.
It is noticeable if you look at the stick while doing this that initially the controls trail in the relative wind, eg if the spin was upright the stick will remain rear of neutral. This is where you want it in the Pitts which suffers from the tail plane and elevator considerably preventing the rudder from getting good airflow over it in an upright spin. This is made worse if the stick is pushed forward prematurely.
Similarly, hands off, the stick is deflected slightly into the roll component of the spin. Again this is where you want it in the Pitts because it gives that wing less drag (aileron up). Perhaps more importantly it gives the other wing more drag.
When the anti-spin rudder (the Primary) and the little bit of in-spin aileron take effect and the rotation slows almost to a stop, the natural stability of the aeroplane takes over.
The stick snaps into the central position by itself and after centralising the rudder you can recover to normal flight. Again, this is what Pitts biplanes will do. Other types may not, indeed some will not.
Therefore, as many others have said, you should follow the flight manual procedure for the aircraft type.
Even more importantly, get dual instruction for spins as they can be disorienting. A neophyte may let the anti-spin rudder come off the stop or even have no idea which way the aircraft is spinning.
Control friction may prevent the ailerons going where they should and in types with considerable ‘washout’ (wing twist) on (for example) high-wing Cessnas an outboard wing may remain un-stalled in a spin. In-spin aileron would be counterproductive in that case.


text:
Are some countries' civil aviation authorities safer than others?
Okay, put down the pitchforks, I'm not pointing fingers at anyone!
I'm just aware that every country has its own civil aviation authority, and I wonder if there's any reason to believe that some countries perhaps have safer standards, and perhaps are more vigilant in enforcing them.  As opposed to, say...the opposite of that.
My assumption is that most countries, if not all, take aviation safety extremely seriously.  And that, as a result, aviation accidents are truly random occurrences that have nothing to do with the country of origin for the flight.
But I may be wrong, hence I'm asking.
NOTE: I am not interested in opinion and personal experience on this.  If you don't have statistics and accident reports to back up what you are saying, please refrain from answering.

A good way to figure this out is to look at the list of air carriers banned in certain countries like the EU which are typically banned because of poor safety standards, regulations, or records. Here is another source for the EU information. The US uses an International Aviation Safety Assessment which also contains the assessment results.

@RonBeyer That's an excellent start to an answer, very resource based.  I'd encourage you to pursue it :)

We can pretty definitively say aviation accidents aren't truly random, but it may be hard to pin down contributing factors from a simple metric like  "accidents per 1000 hours by country of registration." A spike there could be a safety culture problem, or reflective of the kind of operations happening with those aircraft bearing a higher level of risk (extreme environment, hazardous duty, etc.) even when balanced by a strong safety culture. This one is going to merit some complex analysis...

Some countries aviation authority use stricter standard due to conservative policy or bureaucracy.

The most safety aviation authorities is in Palestine------There is no active airport/heliport in there.

Lets take the EU for example. In the EU, there are 230 banned air carriers. The majority of these (228) are banned because the EU CAA has determined that the country in which these carriers operate do not have enough oversight to ensure the safe operation, regulation, and maintenance of the airlines.
Two of the air carriers are banned specifically because of poor maintenance standards, obsolete aircraft, or other reasons.
Similarly the US has the International Aviation Safety Assessment although a much shorter list because it really only evaluates airlines that are codeshare or operated by companies that serve flights to/from the US. For the EU, this is a larger list because it does not require crossing an ocean to get there...
Typically you'll find on these lists quite a few airlines that operate out of developing countries like the Congo or Angola. Its reasonable to draw the conclusion that countries that do not have regulatory oversight for much outside of running the government itself leaves the standards of safety to the operators themselves.
This isn't to say that the operators are automatically unsafe, they just lack government regulation and observation of safety standards.
So to mirror what vortaq7 said in his comment above, quantifying this is going to be difficult since the types of operations vary highly between countries. For example the US has a high accident rate looking at pure fatalities over the last 25 years compared to any other country, but this is because the US is biggest aviation market.
Looking at it in the context of incidents per million flight hours may be available, but it also groups a lot of different types of flights like cargo and commuter. I'm sure this type of data is available for more developed countries with reporting systems and formal accident investigations but may be difficult for countries that don't have that.

And now for a personal note... I know you're not interested in the personal aspect but Angola's air carriers are banned in the EU, so it gives a little credibility to what I say above, plus its a good story. :)
A part of my job is travelling the world and being flown out to oil rigs for work on the automation and safety systems. About 8 or 9 years ago I had to fly out to Luanda, Angola to be flown out to a rig a few hours off the Angolan coast. The flight there (and back) was on the Houston Express, a direct flight from Houston to Angola.
Upon arrival at the Luanda airport, I was taken to the heli-terminal for the flight out to the rig. Now understand that in the US Gulf of Mexico people travelling by helicopter to an oil rig are required to have egress training. In the EU, travelling out into the North Sea also must include cold water survival. In Luanda however, there were zero requirements (I know this because I did not have egress training, nor was I asked to prove I did).
After 3 or 4 equipment delays we were finally boarded on the helicopter, I sat across from the flight engineer and 3 or 4 other rig hands were on board. After take-off and after we flew over the coast, here is pretty much the actual words I spoke:

ME->Flight Engineer: What is dripping on the back of my neck? Smells like fuel.
  FE->ME: It is fuel.
  ME->FE: Should I be concerned?
  FE->ME: Only if it stops dripping, that means we are out of fuel.

Be sure I spent the remainder of the flight studying very carefully how to pop out the egress window...
When we got back to Luanda the aircraft we were supposed to take back to Houston had "mechanical problems" which delayed my return by 3 days. I could see the aircraft on the tarmac and it was sitting on cinder blocks without any tires, literally like you would imagine leaving a nice car in a bad neighborhood overnight. I spent those 3 days in a compound run by the oil company that had 16 foot tall walls with barbed wire and a very hefty front gate.

The problem with incidents statistics is that in the countries with poor safety culture, where the risk is highest, reporting incidents does not work all that well. So in practice the safer countries report more incidents. See this interview with Simon Hradecky, the editor of The Aviation Herald (he mentions specifically Canada as having particularly good reporting).

EU has longer list because it includes airlines on them independent of whether they might want to actually fly to Europe or have any cooperation with airline that does. The list also does have some (small) effect even on airlines that don't try to fly to EU, because it detracts travel agents from booking flights with them.

I know we aren't supposed to encourage anecdotes, but +1 for the 'if it stops dripping' line.

"Two of the air carriers are banned specifically because of ... obsolete aircraft..."  Why would obsolete aircraft be a problem, as long as they're kept properly maintained?

Yes the EU is safest, US next and rest of the world, especially Africa, India and Singapore, are large death traps

authors: Алексей Сергеев


text:
In a Cessna 172 flying VFR on long final, when do I extend flaps to 10, 20, and 30 degrees?
At the pilot-controlled airfield I use most frequently, we fly a standard rectangular pattern.

The normal-landing C172 flap sequence goes

Downwind: 10 degrees past the “abeam point” and airspeed in flap range
Base: 20 degrees
Final: 30 degrees when assured of making the runway

When making occasional landings at a nearby Class C airport, ATC sometimes puts me on vectors resulting in a long, straight-in final. In relation to such an approach, when do I extend flaps to 10, 20, and 30 degrees?

As in any situation: use your best judgement as PIC.  For example, when I fly into a B or C airport in a 172, I might not use any flaps - so I can keep my airspeed up and come in on a low approach as to not disturb the airline traffic as much as possible.

But yes, rule of thumb is to extend the traffic pattern outwards.

Here's what I do in a straight-in: fly it at cruise speed, and at 4 miles out, set power for final approach speed (you do know what that is, right? usually 15-17" or 15-1700RPM in a light aircraft; also, some engines need to be cooled more slowly than going straight from cruise power to approach power).
As the aircraft slows down, keep trimming the aircraft to stay on the VASI, and as you slow to Vfe for the different flap settings, bring those flaps in.
Full flaps should be in no lower than 500AGL for a stabilized approach.
You can adjust the 4 miles to suit your preferences and conditions (slow or faster, depending on skills, wind, and traffic).
"Full flaps when the runway is assured" is a rule of thumb. More important is to not make any configuration changes (flaps, trim, gear, speed brakes) below 500AGL in VFR.
If you learn how to do this, you will fit in with lots of different kinds of traffic, and you won't have the Baron on downwind have to fly 5 miles out because you're doing 60 on long final.
This skill is also worth learning because it you will have a mastery of the landing process and get you out of the slavish "do this, then do that, then do that" type of flying
Good approaches make good landings!

I visualise the standard lengths of the pattern and pretend I'm simply doing them in a straight line.
I'm sure you could figure out precise lengths or time intervals if you wanted to, but ultimately in a 172 in VFR you don't need to be exact - you just need to be fully configured and established by the usual point on final approach, as if you were completing a circuit.
The trap many people find with a straight-in approach is they leave everything too late - downwind checks, flap, etc. Make sure you allow enough room for about 15-30 seconds between flap extension, otherwise you'll find it difficult to maintain the approach angle.
As with everything, a good straight in approach takes practice!


text:
What will the impact to GA be if DTC DUAT goes away?
Data Transformation Corporation issued the press release below.

FOR IMMEDIATE RELEASE
DTC DUAT Contract Extension
May 21, 2015 — Data Transformation Corporation, DTC DUAT which
  supplies the DUAT Service for the FAA for the past 25 years, has
  announced that it has been granted a 60 day extension by the FAA to
  continue to provide the FAA DUAT service. DTC DUAT has always been
  committed to making the DUAT Service better for General Aviation
  pilots by adding new features and services making it easier to get
  weather briefings and file flight plans. DTC would like to inform all
  of its users and third party vendors that we are fully operational and
  plan to continue operations during and after the 60 day period. DTC
  DUAT is pursuing alternative avenues to provide the DUAT Service
  capabilities to its users following the 60 day extension period.
For more information on this topic or anything about DUAT, please
  contact our marketing manager, Doug Priestley, at (800) FAA-DUAT
  (322-3828) or by email at
  marketing@dtcduat.com.

If the alternative avenues do not produce the desired results and DTC DUAT operations cease, what will be the real-world, day-to-day effects on general aviation?

I think that there would be little practical impact, except for those people who are heavily invested in DTC DUATS specifically and have to switch to another system.
First, there are two DUATS providers: DTC and CSC. Even if DTC goes away, CSC is still available, at least for now, and it provides exactly the same service as DTC (see this question).
Second, Lockheed Martin Flight Service (LMFS) provides all of the information and flight plan filings that DUATS does, and also provides briefings with a human briefer. So there is a completely separate alternative to DUATS available, although admittedly switching tools always has some cost in terms of time and learning at least.
I assume the main impact would be on people who use DTC DUATS as their primary flight planning and filing tool and use it directly, rather than via another tool. For example, I use Garmin Pilot with CSC DUATS but I could switch to DTC simply by changing the data provider option. Some flight planning tools also support LMFS flight plan filing and I guess that more and more will in future, if only for competitive reasons. But if you use the DTC DUATS website directly and are very experienced and comfortable with it then switching to LMFS or anything else would have a learning curve.
But in the end, people won't quit flying or even cancel flights just because DTC goes away. They'll just complain a bit, choose a new platform (probably LMFS) and get on with it.

There are many downstream companies that provide briefing services and flight plan filing using DTC or CSC DUATS, and the ones using DTC may have some trouble transitioning to another provider of data. My impression is that more of these downstream vendors are with CSC and will not be interrupted.
For example my company, ENFLIGHT.COM (which provides the time-saving value added service of personal minimums briefing on top of a DUATS briefing) relies on CSC as the back end.
Lockheed Martin is also heavily promoting interfaces to allow downstream companies to provide value added services on top of flight service data and connectivity. I know a number of companies are developing interfaces to Lockheed, at the very least to avoid having all their eggs in one basket.

I believe those of us that found DTC to be the best of the three will be disappointed in the other two.  I miss DTC already.  Lockheed Martin, to me, is as primitive as the Flight Service tools I used for 13 years as a briefer for the FAA. CSC is not much better.  Recently CSC e-mailed me and said they were not interested in any of my negative comments about their system. (They were suggestions).  If there is a commercial briefing system I can afford I would consider it over these two!  If we could follow the money trails from lobbist and not allow non-aviation oriented quota hires to make decisions in the FAA DTC would have easily won over the other two!  I fly only VFR these years, Bonanza, and rarely at night.  I rarely fly to new places and have routes I have flown for years. DTC made briefings to and from these easy to obtain, read and understand.  I was very happy with DTC.

"non-aviation oriented quota hires" is not a constructive characterization.


text:
What are the ANT and ADF modes on an NDB receiver?
I am seeing this in a simulator, so I don't have a manual for it…
On the Bendix King KR87 NDB receiver, the leftmost button labelled “ADF” switches an indicator above it from “ANT”

to “ADF”

When pushed, the needle on the direction indicator indicates towards the NDB (if in range). When popped, it does not, at least for the NDB stations.
So I am wondering, what does this switch change and why it is needed?
(screenshots taken from FlightGear simulator by me)

I suspect it means “Antenna”, for when you just want to listen to an AM radio station. Maybe disabling ADF improves the range for that purpose?

@StephenS, it might be; the simulator does not simulate the audio quality (basically it starts when you get in range), so that effect can't be observed in it.

The ADF consists of two antennas: the loop and the sense antenna. We already have an excellent answer by mins on how the ADF works, so I'm not going to repeat it here. The important thing for this question is the pattern of the two antennas:

(modified from source)
As you can see, the sense antenna has a spherical pattern and therefore sees the same signal strength from all directions. The loop pattern does not (which is what gives the direction information when used as an ADF). The ANT button disables the loop antenna, which means all the signal comes from the sense antenna. This improves the audio quality when listening to a Morse code identifier (or something else like AWOS):

Most ADF receivers have several modes that the pilot can select. If the "ANT" mode is selected, the loop antenna is disabled and all receiving is done through the sense antenna. This mode provides the clearest audio reception, so you’d normally use it to identify a station or listen to Rush Limbaugh. On King ADFs, the needle should park in the 90-degree position when the receiver is in "ANT" mode; other brands may work differently.
In the "ADF" mode, the pointer is activated and the ADF tries to point to the station.

(AVweb - ADF Basics)

ANT mode improves the audio reception when listening to a station's morse code identifier or whatever else is being broadcast.  Normally the directional needle gets parked at 3 o'clock when in ANT.  NDBs can also have other broadcasts besides station ident, like ATIS or AWOS weather data, etc., and in some cases use of ANT may make the difference between making out what is being said, or not.  It may also improve AM radio audio reception, but not sure.  I've used the ADF to listen to music back in the day, but never had to go to the trouble to switch to ANT to hear it.
Here's a link to a KR 87 manual.


text:
What are the disadvantages of a Tail providing lift? (tandem-wings included)
Most aircraft feature the tailplane configuration, which requires the main wing to provide higher lift than the weight of the plane itself, what seems counterproductive.
Few aircraft have featured tandem-wings like the Rutan Quickie, Proteus or the Maurice Delanne 10 with limited success. I usually read that the main disadvantage of the tandem-wing is that the rear wing is subjected to the downwash from the front wing, what greatly reduces its efficiency Q&A link.
My point it that standard tails suffer from the same downwash effect, and on the other hand this effect can be reduced by:

a T-tail
Making the front wing much larger than the aft-wing.

Thus, which are the flaws of this design (top)?
Given that it could still have the CoG in front of the Neutral Point.
Why are lifting tailwings refered as unstable? Q&A link
Is this layout suitable for VTOL aircrafts, in which horizontal take-off and landings are not an issue?

Thank you for your attention. I would appreciate remarks of any wrong assumptions.
Extra

Why the Proteus features a tandem-wing, and why this layout unusual?

Edit:
The reason for considering a lifting tail is that to make VTOL possible for this layout, the CG must be moved between the rotors, thus far aft.

That planform diagram looks like a conventional wing and tail design to me.  What is different about it?  In fact both designs pictured look very conventional...

the section about pitch wise stability of how it flies is a good reading tp better understand your question.

I think birds get lift from their tails. Fuel is more expensive but the "avian-onics" are better, so stability is less important. I think.

Focusing on the aircraft in the picture, lifting tail aircraft are essentially bi-planes.  The single lifting wing has proved to be more efficient long ago.  Simple adjustment of the CG removes the need for a lifting tail.  This plane could be flown that way.
It is the job of the tail to set the wing at a given AOA, using aerodynamic force in flight to hold that AOA.  The thought of tail "downforce" creating a huge lift penalty is not true.  In flight, it is the angled, lift producing wing that creates the "induced drag", while the tail rides along at its lowest drag.  Torque around the Center of Gravity keeps it that way, unless some disturbance changes the wing AOA.  Many aircraft, like the Piper Cub, use a low aspect flat plate as a horizontal stabilizer, with an elevator to create a crude, but adequate "tail wing" to change pitch or trim as needed.
Only when CG is placed behind the center of lift does a lifting tail become necessary, but directional stability is affected because now more wing and fuselage area is ahead of the CG.
Many planes on the ground show the "decalage" of the tail appearing to provide a lot of downforce, but in the air it will "weathervane" into the wind, torquing the wing to the desired AOA.
Moving the weight forward on that model needs only adjusting the fore and aft engine thrust percentages for VTOL.  In the air, treat it like an airplane, with one lifting wing and CG slightly forward.  And yes, keep the T-tail.
An add on for those who wish to further understand lifting tails.  The whole point of a tail is to increase directional stability.  Taking a wing without a tail, and balancing the center of lift with the CG still will have some directional stability because the center of lift is usually at least 2/3s of the way forward and the back portion of the wing acts as a "stabilizer".   Add a tail to this and you are far more directionally stable, and there for able to move CG behind wing center of lift and still have directional stability.  This is by no means fatal in all cases, but will make the plane less stable and easier to turn.  Good for fighters, not for cruisers.
For the modeler building the VTOL above, no need to get stupid when simpler solutions are at hand.  Make it an airplane first, and use differential thrust for VTOL.  At least 2 of the motors could be idled in cruising flight.
Regarding the Proteus, Rutan wanted a high flying heavy lifter.  A very high aspect wing is most efficient, but presents structural challenges.  So he made a bi-plane.  Colonel Pezzi flew one to 51,000 feet in 1937.  With Rutan, one strives to understand function as well as form.
PS. A lifting tail is entirely safe as long as the CG is within design limits.  The XB-70 certainly is a "lifting tail".   People get into trouble moving CG behind design limits because they use up elevator throw to create lift and also make the plane less stable than it is designed to be.
But take a model of an XB-70 to the hill and fly it off with an average sailplane model of equal weight and wing area.  No contest for gliding efficiency, but the XB will have a much wider speed envelope under power.

it's Center of Gravity applying torque about the Neutral Point (Center of Lift adjusted to account for external moments increasing or decreasing the torque).  Gravity acting at the C of G is the force APPLYING the torque.  Move the CG aft to the NP and the torque goes to zero.

@JohnK you can take moments about any point of a solid as long as the sum of forces on that solid is zero. Taking them about the center of mass is advantageous because it removes one of the moments.

@John K interesting that you mention that (twice).  Theoretically, both explainations work, and yours was actually favored because it provides an easier explanation for static stability.  However, the effects on moving the CG back on the plane are the same no matter how we explain it theoretically.  That plane in the picture looks like a winner to me, maybe with a hair more dihedral.

My point is moving the GG fwd increases the torque, increasing tail downforce reqmt, and moving it aft decreases it. When CG is at NP, torque is 0 and tail downforce required is 0, a rather unstable craft. Keep going aft, to a negative value, forcing tail to lift up to keep the nose down, you have a fatal condition normally. Lifting tail airplane is really a tandem wing with a small aft wing; problem becomes how to get a desirable pitching tendency w speed; slow down pitch down, speed up pitch up. Canards do this by having a steeper lift slope for the front wing by using a different airfoil.

@John K yes, if CG is forward some down force is required, but not necessarily 100s of pounds.  The plane pictured, especially as a model, with mixing of forward and rear VTOL thrust, would fly well without the need for a lifting tail.  Sort of reminds me of another way to make an Avro Lancaster, which flew well enough to gain admiration from the fighters.

A lifting tail just means lower static stability.
You are correct, flying in the downwash of the wing makes the tail less efficient. But that does not mean it is all bad: Since downwash increases with lift coefficient, the tail effectively sees a smaller angle of attack variation than the wing, so it maintains a healthy margin from stalling even while the wing is stalled. This helps to keep the aircraft controllable well into a stall (within limits, of course).
The reduction in downwash as the center wing stalls will even add a positive AoA gradient during the incipient stall which adds some more stability, making it harder for the pilot to command a further AoA increase.
And performance-wise, the download on the tail in conjunction with downwash actually might create a bit of thrust on the tail.
Concerning Rutan Designs: Their different looks are not for better performance but merely the expression of an oversized ego and his way of self-promotion.

EDIT:
The many downvotes I now collect for speaking my mind freely shows how well the self-promotion of Burt Rutan works. But it cannot bend the laws of physics which guide my opinion. Which I will continue to express freely.

I've been following Rutan since the 70s and I've always had a similar take.  His brother, a former F-4 pilot who once did a record endurance flight in a Long Eze where he had fatigue induced hallucinations during the overnight part, is pretty much the opposite.

@JohnK -- "where he had fatigue induced hallucinations during the overnight part" -- just like Lindbergh on his 33 1/2 hour flight...

Yep I read Lindbergh's book.  He crossed the Irish coast only a couple miles off track in spite of having dozed off, and wandered this way and that before waking up, numerous times.  I guess his wanderings all evened out.  He also had plenty of fuel left when reaching Paris and mulled over continuing to Rome, but the thought of crossing the Alps at night was enough to squelch that idea as maybe pushing his luck just a little too much.

@JohnK: What I remember most of Burt's brother is his foul language. He called every aircraft a "flying piece of excrement". That does not endear me to him. But to his credit I have to admit that he flew Voyager for a week. Jeana did not do much flying but was there to keep Dick awake.

One cannot write off the record-breaking achievements of  a plane like the Voyager as down to "the expression of an oversized ego and ... self-promotion." It was a brilliant piece of aircraft design. Burt Rutan cannot be written off just because you personally object to his style.

@m2as3registeredservicesohmone Since you are not aware of the irony of criticizing someone for being critical: You do exactly what you slam others for. Regarding aircraft: I've brought 3 in the air so far. What's your count?

It is not actually true that

... the tailplane configuration ... requires the main wing to provide higher lift than the weight of the plane itself

What matters for stability is that the change in lift moment of the tail should be greater than that of the main wing; the absolute value of its lift is not relevant.
The lifting tail has been well understood since around 1918.
In a tandem wing, both planes provide lift. Now consider the rear plane being progressively shrunk to the size of a tail plane. It is quite false to imagine that it must necessarily pass through a zero-lift condition at some point and end up with downforce. Practically, it might do, but that is another issue.
The tail creates least drag when it has zero angle of attack and for maximum economy the aircraft is trimmed to approach that condition (although, as pointed out in another answer, operation in the wing downwash can make a small downforce the ideal condition). However trim frequently changes during flight and the ideal condition is seldom met in practice, and then only transiently as the trim adjusts from one side of the balance to the other.
What often confuses students is that the wing must be designed for maximum lift at the moment of rotation for takeoff, when it is fully laden at its slowest flight speed and the tail is pushing down strongly to rotate the nose up. But that condition is only transient, it soon passes and the cruise condition is quite different.

A conventional aircraft with the CG aft of the neutral point, required if you want to make the tail make positive lift, has a negative static margin and is unstable in pitch.Trim Drag is the energy lost in creating downforce due to the positive static margin and you can minimize it but can't eliminate it because you have to maintain a positive static margin unless you have artificial stabiltiy. This idea of cruising with a lifting tail, on an airplane not designed as a tandem wing aircraft from the start, is crazy. https://www.boeing.com/commercial/aeromagazine/aero_02/textonly/fo01txt.html

To someone who does not appreciate the difference between lift moments which resolve around the centre of lift, vs changes in lift moments which resolve around the aerodynamic centre, it might seem crazy. To others, including experienced pilots I have discussed it with, trimming the tail for positive lift is a familiar and safe phenomenon. https://en.wikipedia.org/wiki/Aerodynamic_center

To trim the tail for positive lift the CG must be aft of the NP.  If the CG is forward of the NP, there is a ND pitching moment and making the tail lift just adds to it. Static margin requires CG to be a minimum distance ahead of the most forward NP.  I don't know where you are getting this from and cannot find any source anywhere that says a conventional tailed aircraft can operate with the CG aft of the NP, except aircraft with artificial stability designed to operate in an unstable state for maneuver purposes. If you have a source, NOT wiki or ASE, that covers this, I'm all ears..well eyes.

Sorry, your conclusion is just plain wrong. There is not space for the analysis here but I urge you to consider the marginal case between a tandem with small real wing and a conventional tail; what changes and why? More importantly, what does not change? What effect does a lifting rear surface have on the NP? Understand these and you may yet get there.

Well for starters, with a tandem/canard the stabilizing surface with the steeper lift slope and variable camber element, the "elevator", has to be on the forward lifting surface, with the NP between them and the CG, still, forward of the NP.  You don't seem to understand the basic difference between a tandem/canard and conventional tail, and won't address my question directly.  Fine.  Provide a link to an authoritative source, NOT an anonymous wiki or another ASE post, somewhere like NASA or a university source, that describes what you are saying.  It should be easy.

Westland's designer WEW Petter put the elevators on the rear wing of  the tandem-wing Lysander. Test pilot Harald Penrose tells us on page 199 of his autobiography Adventure with Fate that he first flew it on 27 July 1941 and it "proved even more stable" than the conventional Lysander.

Interesting. Although a bit of an outlier I'm curious to learn more. Rutan's big achievement was getting a canard/tandem to have desirable characteristics, which was elusive because the desirable lift slope of a thin stablizer surface didn't work so well with lifting stabilizer at the front that was carrying significant loads.He used an airfoil developed at U of Glasgow, with an odd sharp nosed flat bottom heavily cambered profile.  Problem was it didn't like surface contam and would lose lift in rain, which plagued his designs until John Roncz developed an airfoil that solve the rain problem.


text:
Are aircraft still guided by ground marshals?
Are ground marshalling operations still conducted by personnel on the ground? Are there any airports that still do this procedure?

From Wikipedia.

Please, in which countries would like to know about?

Mmm. I  want to know more or less in which countries they still do this kind of operations.

I can say that in Brazil, in some domestic and military airports they still use the marshalling.

I've 2 close votes because it's unclear what I'm asking. Just tell me what is unclear and I will edit the question

Are you talking about a "Follow Me" vehicle escorting the aircraft, or are you talking about ground handlers (as in your picture)?

The type of marshaling in your picture (ground crew with hand signals) is done at every major airport I've ever visited. The ground personnel have to tell the pilot how far forward to pull the aircraft when coming up to the gate. Its also done for GA aircraft at FBO's to direct them where to park quite often.

I understood the question, although from an American English perspective it was strangely worded until an edit that happened while I was writing this comment. I up voted the question because I'm curious as to how much things have changed since I retired in 1999. Back then we were often marshaled, especially in third world countries. Even in the U.S. we were usually marshaled when coming in to everything other than a jet bridge that had electronic guidance as to when to stop.

Typically, marshalling is used to guide aircraft to their parking stand.
There are alternatives available (Visual Guidance Docking Systems) that allow pilots to park their aircraft at the right spot without the aid of a marshaller.
In its simplest form, the parking spot has a big identifier to allow the pilot to select the right stand, a centreline for the nose wheel to follow, a marking where the nosewheel should stop and a mirror so the pilot can see where the nose wheel is relative to the marking.
In its more advanced form, there are pressure plates in the stand that determine the position of the aircraft, a laser scanning system that determines the exact position of the aircraft and whether the stand is obstacle free, and a digital display guiding the pilot during parking.
In case the VDGS is not available or cannot handle the specific aircraft type, a marshaller will have to step in.

When taxiing into the FedEx hub in Memphis there was always a very simple guidance system. There was a rubber bar hanging from chains to tell the pilots where to stop. They would aim for it and stop when the center window post touched it. Other than that I never noticed any kind of system to tell them where to go. No marshaller. Just lines and that rubber bumper. Could be that they just didn't need to be all that precise since all the loading equipment moved.

The APIS system is in place at many United gates at ORD (Chicago O'Hare). BTW, I've never seen a mirror to see where our nosewheel is. Doesn't mean they're not out there though!

would be fun in windy conditions with the ball jiggling about.

For what I know, the EAA AirVenture still uses this method. I have heard from a few friends in the Civil Air Patrol about this.

Yes, EAA (and many fly-ins like Sun-N-Fun) use marshaling to keep aircraft separate and get them where they need to go quickly and without interaction from ATC which would be busy with incoming flights.


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What is the purpose of Runway Grooving?

What is the purpose of runway grooving?
How does the airport drainage system work?
Why do airports remove rubber from the runway?

Rubber removal is addressed here: Do runways need some special kind of tar or protective layer? and How often do runways need to have typical maintenance?

This is three almost entirely separate questions. Stack Exchange tends to work best when there's only one question per question

What is the purpose of runway grooving?

The channels help to remove water from the runway. They also provide an area for the water to build up. With out these channels the water runs the risk of forming a thin surface covering the runway which can be very dangerous. As mentioned by john here in the comments this is usually known as hydroplaning and is the same as what happens to a car.

How does the airport drainage system work?

This is a bit of a guess but I assume they work like any other road drainage system and it will depend on where the airport is located. Here is a very dated report prepared for the DOT on runway drainage that you may find of some interest. Here is the FAA's full paper on designing surface drainage for airports, it's a bit long but should cover what you are looking for.

Why do airports remove rubber from the runway?

Tires obtain the best friction when they come in direct contact with the runway surface. Excess tire rubber that wears off and sticks to the runway can affect the tire/runway interactions. This wiki article covers the main points pretty well.

Wet rubber on the runway is especially slippery. Race cars have the same issue, and you will see drivers using the "wet line" or "carting line" when the track gets wet so they can avoid the build up of rubber on the track that is very beneficial when dry.


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What are these little things on the evacuation slide?
I marked them with black circles. What are they for?

Source (modified)

in raft mode I'd guess a place for the tent to prop itself up with

Those are where the ladies hang their hand-bags on the way down.  :)

@ratchet freak is correct. The protrusions are canopy poles, where the canopy in the evacuation slide/raft is propped up. The image below shows a canopy propped on them.

Image from tulmar.com
From the document:

The canopy is supported in the center in 4 places by inflatable yellow “CANOPY END SUPPORTS” and “CANOPY CENTER SUPPORTS”, and supported along the sides by 14 numbered supports on the top of the slides inflatable structure.

Here's a closeup of the support from the same document.

Has there ever been an actual event where a slide was required to be used in this way?

where is the actual canopy stored?


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What activities take place in the warning areas offshore of Washington, D.C.?
Looking at the Washington sectional, several areas offshore are designated "Warning" areas: W-386, W-107, W-105 etc. The only notes given are "National Defense Operating Areas. Operations hazardous to the flight of aircraft conducted within these areas".
That would be enough to keep me well ashore, but out of morbid curiosity, what kind of activities are we talking about? Are these areas designated for naval gunnery/missile ranges?

Answering my own question, these areas are designated for a variety of naval training and testing exercises including missile launches and heavy guns firing, which is the primary reason it's hazardous. The airspace can be traversed under guidance from either Washington Center or FACSFAC VACAPES, but entry by VFR aircraft without established comms is not recommended.

Out of interest, where did you find the answer, and is similar information available for all warning/restricted areas?

Here's one such reference: http://wiki.radioreference.com/index.php/Giant_Killer "Giant Killer" is the callsign for FACFAC VACAPES, the military facility controlling most warning areas off the coast of Maryland, Virginia, Delaware, etc. including most of the ones I mentioned. I originally got the information from a PDF of a brief of the facility and the changes to the FAA rules for the airspace (these areas used to be totally off-limits when active but that caused congestion through the air traffic lanes between the zones).


text:
Does the air resistance of a jet engine air intake count towards the jet's total air resistance?
Does a jet engines air intake count to the overall jets geometry dependent air resistance?
Taking the Saab Tunnan as an example it's overall air resistance has to be quite low because of it's huge air inlet.
Or does the inlet create air resistance as well but just not so much?

I'd venture to say that its supposed to create air resistance. You need to lower the speed of the air entering the engine, especially in supersonic jets to a sub-sonic speed before it goes into the compressor stage.

I'm no expert, but I've heard that the shape of the intake is important. They bolt on a special intake when testing engines in a test cell, which allows the air to enter "cleanly". If the air has to turn a sharp corner coming in, it doesn't flow properly.

Yeah you have to bring the air to the whole fan. Not just a part of it. If the intakes geometry isn't well designed it could happen that the air flow just hits the middle of the fan and as a result also only the middle of the compressor fans. You have to make sure to hit the whole fan with air. Otherwise its inefficient.

This is a very tricky topic. Basically, you need a clear definition of what is part of the engine-related drag and what is counted towards airframe drag. Splitting up drag between components will always produce an arbitrary result.
An intake can generate thrust as well as drag. In case of the SR-71 at Mach 3, the intake contributed 54% of overall thrust, if you just look at the pressure distribution over the intake walls.
Generally, the job of the intake is to feed air to the engine compressor at just the right speed and as homogeneously as possible. This requires it to suck in air when at rest from all around the aircraft, and to ingest only the core of the stream of air flowing towards it at high speed. What is not ingested needs to flow around the intake lips and the engine fairing, and the drag caused by this process even has its own name, being called spill drag.
At high speed the intake needs to slow down the oncoming air and does so already ahead of the intake lip at subsonic speed. At supersonic speed this slowing down is accomplished by shocks, which adds another source of drag. This can be easily counted as part of the airframe drag, but done right this slowing down will compress the air, which in turn will increase thrust. Apart from viscous losses, this compression pays for itself and is almost drag-neutral in a good design and at ideal conditions.
Next is the flow around the intake. Just throttling the engine will change the airflow through it and thus the flow pattern around the intake. You can imagine that some configurations show marked changes in aerodynamic drag depending on the throttle setting. In case of the Eurofighter, the vicinity of the canard will even cause throttle changes to result in notable pitch moment changes.
To answer your question: Yes, the intake will produce drag, and how much it does depends on how you define drag. It is certainly wrong to think that the stream tube hitting the intake will just disappear into it and not add any drag.


text:
Why do some non-precision approaches have stepdown fixes after the final approach fix?
Some of the non-precision approaches have a stepdown fix after the final approach fix. My understanding of a stepdown fix with an altitude restriction is that it is to keep you clear of obstacles before continuing your descent right? However, why does it so happen that some stepdown fixes are after the final approach fix rather than let the final approach fix be the "stepdown" fix of an approach?

Can you give a specific example of an approach? It would help to make your question clearer.

It sounds to me like you're asking "why not call the last fix on the approach the final approach fix, no matter how close it is to the airport".  Have I misunderstood your question or is that mostly correct?

Yep, Steve is right on the ball.

Take a look at KPRB VOR Rwy 19:

There is a stepdown fix after the final approach fix. Now look at the terrain around the airport. You can see a bunch of small hills around the FAF. In order to provide adequate terrain separation and get you low enough to land, they need a stepdown. You can also see this on lots of non-precision approaches where the approach minimum is lower if you can identify a point past the FAF.
If you are interested in how they decide to include a stepdown fix, check out FAA Order 8260.3C TERPS, Section 2-6. Final Approach. Lots of formulas but the gist of it is they have a required obstacle clearance that must be met and maximum descent angles. Sometimes they need a stepdown fix in order to make the approach work.

To address the part of the question

why does it so happen that some stepdown fixes are after the final approach fix rather than let the final approach fix be the "stepdown" fix of an approach?

The answer there is, the final approach segment (FAS), defined as the final approach fix (or, on glideslope at glideslope intercept altitude, for an ILS) to the missed approach point, has to be a certain length, and if the stepdown fix were made into the FAF, the FAS wouldn't be long enough.
In the chart that JScarry posted for KPRB, the FAS is 6 miles long, which is fairly typical.  The distance from the stepdown fix to the MAP is 3.7 miles, which is awfully short -- probably too short to be approved without some strange waiver.  The "interior stepdown" ends up being the better solution for the approach designers.


text:
I have an FAA ATPL based on a foreign ATPL, can I convert it to an EASA ATPL?
I have an FAA ATPL based on my Foreign ATPL. Am I now able to convert my new FAA ATPL to EASA ATPL? Of course with me doing all the exams etc..
or am I only allowed to convert my original foreign ATPL to EASA?

When you say convert do you mean you got an FAA ATPL on the basis of your foreign ATPL, or that you took the FAA tests?

I mean I got an FAA ATPL based on my Foreign ATPL..

Is your FAA ATP unrestricted, or does it say it's only valid together with your foreign ATP?

What is the difference between the restricted and unrestricted? I mean i completed the ATPL CTB course and skill test with all the requirements

Maybe restricted is the wrong word, but in the past I had an FAA private license issued under 61.75 based on a South African one. It had this restriction: "ISSUED ON BASIS OF AND VALID ONLY WHEN ACCOMPANIED BY SOUTH AFRICA PILOT LICENSE NUMBER(S) xxxxxxxxxx.
ALL LIMITATIONS AND RESTRICTIONS ON THE SOUTH AFRICA PILOT LICENSE APPLY" I was wondering if your FAA ATP license has something similar on it. As far as I know an ATP cannot be "based on" anything, it's always valid by itself.

Ok. I know there are piggy back FAA PPL licenses and there are also stand alone FAA PPL licenses. Both can be achieved by converting a foreign license. Is there the same thing for the ATP conversion? I thought the ATP would be a stand alone license or is it not?        For example I was told by the UK CAA that i could convert a standalone ppl license from FAA TO EASA but not a piggyback. So this is why im asking if a FAA ATP is also a piggyback or not?

@mizzu what does it say on your FAA ATP certificate? If there limitations they'll be printed on that card. What do they say?

Do you actually have an ATPL or a frozen ATPL?
Essentially, EASA requires you to sit all the ATPLs as well as the individual IR exam and your practical flight tests for the CPL, ME and IR. That is conditional on you having completed an "approved course of training" and whether your FAA stuff counts I don't know; I doubt it as it isn't EASA.
Some stuff (CPL, ME & IR) can be converted depending on experience but from what I understand from a friend, many UK schools are very reluctant to do this at all. I can't speak for other EASA nations.
So essentially, plan on doing your ATPL again.


text:
What is the best way to remove stuck screws from Cessna wing tank cover?
We need to replace the fuel tanks on a Cessna 150 and the screws holding the wing cover won't come out. They are just frozen in place. I think that the paint also may be working against us: Getting the paint out of the screw heads has been difficult. So far no screw heads have been rounded off.
Have any of you had this problem before?
Also, how is the female part under the skin made? Is it like a j-clip nut that can be replaced, or is the nut part a pressed into the frame?

Absolutely agree with @rbp, even if the local laws allow you to work on an airplane yourself you shouldn't do it unless you are qualified.

Then upvote my answer :)

According to the parts manual, there are four types of screw securing the tank cover but no nuts, clips, etc. So the threaded part must be integral to the airframe.

@RedGrittyBrick I don't have a 150 service manual, but based on this photo it looks like they use nutplates to secure the plate around the filler neck, and either rivnuts or something similar around most/all of the panel perimeter. (So if someone gets to Step Four in my answer below be extra careful with the drilling-out because if you wreck the piece the screw fits into you may be in for a lot of work fixing it)

First the standard disclaimer: If you're in the US and you're not a licensed A&P mechanic, take the plane to your mechanic. (If you're working with your mechanic on this job and helping out by removing the cover plates you've reached the point where it's time to go tap them on the shoulder and ask for help, because the steps to remove frozen screws can do serious damage if you mess up).

Disclaimer over, on with the answer:
Frozen screws on infrequently-opened access panels are pretty common, and there are a few ways to get them free. You'll note I've drawn a line in this answer: Anything above the line you can probably do on your own, if you have to move to the techniques below below the line let your mechanic do the work (at least until you're confident you can do it without messing up).
Step one for removing a frozen screw is to make sure they're not painted in place - you'll need a paint cutter (your mechanic probably has one) and/or an x-acto knife. Cut the paint around the head of the screw using the paint cutter (or the x-acto knife and a very steady hand), and use the x-acto knife to clean out the screw head so your screwdriver can get a good grip.
Sometimes this is all it takes and the screw comes out on the next try. If not, keep going.
Step two for removing a frozen screw is to use a "penetrating lubricant" - Kroil is commonly used, and Corrosion-X can also do a good job (more about that later). Put a little on each screw and let it work its way into the threads for a while (15 minutes is a good starting point), then try to break the screw loose again. It may take more than one application of penetrating oil to do the job.
Two notes about penetrating oils: One, they need to be able to get to the threads in order to work (that's why step 1 involves cutting the paint). Two, don't use one that contains silicones (they will embed in the metal grains and make future paint jobs a major pain).
Hopefully the penetrating oils will work, otherwise you're going to move on to more destructive processes.

Step Three involves getting a little more aggressive with the screw in question. Typically by the time you get here you've at least slightly damaged the head trying everything else, so grab a grinder or dremel and cut a flat line into the screw head. This will give you purchase for using a regular (flat-blade) screwdriver, which will hopefully let you apply more torque to the screw. You also want to keep applying penetrating oil while you do this.
The trick to Step Three is cutting the head deep enough that the blade won't cam out, but not so deep that you compromise the head-to-shank connection in the screw and snap the head off when you try to turn it. This is a bit of an art, so it's best to have your mechanic step in at this point. If you screw up here you're on to step four, and you don't want to get to step four. . .
Step Four is drilling the f#!@ing screw out. When all else fails you take a drill right through the screw, demolishing it. Your mechanic almost certainly has appropriate drill bits for this, and the skill to do it without seriously messing up the screw hole / nut plate / cover panel / surrounding skin.
Even a skilled mechanic may damage rivnuts or nutplates drilling out a screw, and will then have to replace the damaged piece before a new screw can be inserted.
Avoiding the problem in the future
Once you get the screws out (and your mechanic will - eventually - mechanics always win when screws pick a fight) there are some steps you can take so the next person who has to get this panel off doesn't suffer as much as you did.

Don't paint the screws/panel in place.
If you damage the paint getting the screws out touch it up and let the touch-up cure before you put the panel/screws back on so the paint isn't acting as a glue holding it all together.
Also for the love of sanity don't paint the screws - See #2, and if you repaint the plane do it with this panel off.
Replace the standard screws (probably cad-plated steel) with stainless steel screws.
Stainless screws will corrode, but they're much slower at it than the cadmium-plated steel screws (the cadmium plating that keeps them from rusting in place gets rubbed off as you screw them in). Stainless screws also don't need to be painted like the cadmium-plated ones do, so you won't have to pick paint out of the screw head.
Apply a corrosion treatment before reassembly.
Blast the nutplates/rivnuts/etc. with Corrosion-X or similar - also try to hit any other areas you can reach while the panel is open and things are apart.
Apply a corrosion treatment to the airframe regularly.
Less important if the aircraft is kept in a hangar, but for aircraft tied down on a ramp having a corrosion treatment done every few years will help keep screws from freezing in place.

Is reading disclaimer optional?

@Farhan Reading everything is optional, but when the nice folks from the FAA shows up they tend to print out such disclaimers, roll them up into a tube, and use it to whap the people who didn't read them on the snout.

Hmmmm... Sounds like a job for...SUPER MECHANIC!!! FASTER THAN A SPEEDING LEARJET! MORE POWERFUL THAN A J79! ABLE TO LEAP SMALL PIPERS IN A SINGLE BOUND!!! And remember...KIDS! DON'T TRY THIS AT HOME!! THESE PEOPLE ARE PROFESSIONALS!!!

@BobJarvis If you like your mechanic (and want them to keep liking you) it's also probably a "Buy your mechanic a bottle of their favorite drinkin' stuffs when they're done" job - at least if there are a large number of frozen screws involved.

@voretaq7 - ...with emphasis on the "...when they're done". :-)

Step 0.25: use a speed handle, it will allow you to apply a lot of downward pressure to keep the bit in the screw-head while offering great leverage for rotation. Do not use any type of ratching device until torque is broken. Step 0.5: use a brand new bit, it will grip better. Also have a selection of different #2 phillips bits. Different mfgs of bits grip differently. some better for some screws, others better for other screws. test fit each one and choose the best. Step 0.75: put a little bit of valve grinding grit on the bit. It will grip the head of the screw better.

FAR Part 43.3 describes who may perform this kind of repair on an aircraft. I recommend you take the plane to such a person who will know exactly how to to perform this repair, and allow the aircraft to remain airworthy

Doing anything with sheet metal fastening systems is extremely delicate.
First of all, I would strongly recommend not doing anything mechanical, like use metal scrapers, dremels, gouges or anything like that.
The first step is to use a chemical paint stripper to remove excess paint. Use wood (like a toothpick) if any scraping is involved. Never use a screwdriver to try to gouge out paint.
To loosen the screw use heat. I would use a soldering iron of the type used for plumbing. Make sure have a stand for the iron. Do not just lay it on the ground (or worse, on the plane). Touch the iron to the screw to heat it up, then try to unscrew it gently. If one application does not work, use an ice cube to cool it down, then heat it up again.
Just FYI, this is the way auto mechanics get off tough nuts and screws. They grab a torch and fire away. Obviously, with an aircraft you want to be a lot more delicate, but the principle is the same.

Heat is a good option but I'm inclined to avoid it (even electric heat like a soldering iron) near the fuel tank. Even with the tank drained there may still be enough vapor wafting around to cause trouble (probably not, but a little paranoia never killed anyone).

@voretaq7: Empty tanks are more dangerous than full tanks, because they contain a ready fuel-air mixture. Draining, then filling the tank with argon or carbon dioxide before heating anything near them would be a good precaution. Both are heavier than oxygen and will displace it.

Actually, as a former automotive technician we would warm engine if possible, not the fastener.  The fastener we would cool with ice, as you state. This ensures that the hole is as big as possible but the fastener is as small as possible. Oh, and warm fasteners snap and strip a bit more readily.

Also, after hitting the fastener with a corrosion oil (not WD-40) we would give it a few taps with a ball-peen hammer. This helps vibrate the bits and let the oil penetrate deeper.

@PeterKämpf Yup. Properly purged you could mitigate the risk.

@dotancohen They make convenient tools for doing this with bolts too - none I'm aware of for screws, though a few gentle taps of encouragement with the ball end of said hammer might prove coercive :)

Actually, I do mean bolts and not screws, in Hebrew they are both the same word בורג. And if you are using special tools, then you are in a world of pain as the tools require space around and in front of the fastener, which you don't typically have. There is nothing as frustrating as draining an AC system or radiator, or removing the motor mounts and jacking the engine up, just to get a stripped starter motor bolt out. Ah, I'm so glad that I'm in software now where things are easier...

Just went through the pain in having to remove the leaking right fuel tank from my 1975 C-150M during an annual inspection.  I've owned the plane 3 years. All 46 screws for the skin and cap plate were frozen and covered in several coats of paint. Tried step 1--No joy. Tried step 2 with PB Blaster--No joy. Tried step 3--Nada.  The IA had to drill out most of the screws (a few backed out using left-hand drill bits). It was a 2-day ordeal.  Also discovered one of the two retaining straps was broken and (unknown to me) inside the tank there was a half-melted plastic fuelHawk gauge, a yellowed flexible plastic gas tank filler cap and the gas cap chain.  IA suspects all have been in the tank at least a decade or more. Got the top skin back on today and finished the annual. The culprit turned out to be a leaking sending unit on top of the tank--undetectable until we got the entire skin off. If I ever re-paint the wings, I'll paint all access panels separately and use stainless steel screws. After a couple annuals, the pain is going to come off the screws anyway.

authors: Bob Jarvis - Слава Україні